As one type of the thermosetting resins, varieties of the unsaturated polyester resin prepared by reacting an unsaturated dicarboxylic acid or a mixture of an unsaturated and a saturated dicarboxylic acid with a glycol to obtain an unsaturated polyester and dissolving the unsaturated polyester in a polymerisable monomer such as styrene have hitherto been developed and have found wide uses in such fields as fiber reinforced plastics.
However, in such an unsaturated polyester resin, two opposing requirements of high elongation and high strength of the cured resin have never been satisfied simultaneously and the prospect for satisfying the both requirements is estimated to be very poor.
In recent years, some urethane modified acrylate resins have been developed as novel thermosetting resins. These resins, however, failed to satisfy the two opposing requirements of both excellent physical properties such as high elongation and high strength and excellent corrosion resistance of the cured resin.
As an example of the above urethane modified acrylate resin, the Japanese Patent Publication No. 14,805/1964 discloses that a curable urethane modified acrylate resin useful for adhesives and coatings which is obtained by reacting an organic isocyanate containing one or more isocyanate group in the molecule with an equivalent amount of an .alpha.-substituted monoacrylate of glycol is homopolymerized or copolymerized by using an initiator with the other vinyl compound to obtain a polymer. The organic isocyanate specifically shown in the above patent is a pure organic diisocyanate or a compound derived by reacting a polyhydric alcohol such as ethylene glycol, polyethylene glycol, trimethylolpropane and unsaturated polyester glycol having an average molecular weight of 1000 with an excess amount of organic diisocyanate. When a pure organic diisocyanate is used in the above reaction, however, a resin of neither high elongation nor high corrosion resistance can be obtained. When a compound derived by reacting ethylene glycol and an organic diisocyanate is used in the above reaction, the resin obtained is of inferior elongation, hard, brittle and also inferior in corrosion resistance. When a compound derived by reacting polyethylene glycol and an organic diisocyanate is used in the same reaction the resin obtained is inferior in heat resistance, corrosion resistance and hardness. When a compound derived by reacting trimethylolpropane and an organic diisocyanate is used in the same reaction, the resin obtained is not sufficient in elongation and inferior in corrosion resistance. When a compound derived by reacting an unsaturated polyester glycol and an organic diisocyanate is used in the same reaction, a resin of high elongation cannot be obtained.
As another example, the Japanese Patent Publication No. 15,629/1970 discloses a coating solution which consists of a vinyl monomer and a urethane modified organic resin and is useful as a radiation curable paint, binder, wherein the urethane modified organic resin is prepared by reacting a polymer containing hydroxyl group with one isocyanate group in the diisocyanate to form a polymer having an isocyanate group at the end of the molecular chain and thereafter reacting at least a part of the remaining isocyanate group in the above diisocyanate with a acrylate or methacrylate containing hydroxyl group to introduce some .alpha., .beta.-olefinic unsaturated bonds separated by two urethane bonds from the carbon - carbon main chain in the above polymer. In preparing the above coating solution, the polymer containing hydroxyl group is either an unsaturated polyester or a saturated polyester. When an unsaturated polyester is used, a resin of high elongation cannot be obtained. When, on the other hand, a saturated polyester, specifically a polyester consisting of a polyhydric alcohol and an aliphatic dicarboxylic acid such as succinic acid and adipic acid is used, the resin obtained is inferior in heat resistance and corrosion resistance.
A further example is the Japanese Patent Publication No. 28,533/1973 which discloses a solution consisting of a urethane prepolymer and an ethylenically unsaturated monomer useful as a light curable coating composition, wherein the compound obtained by reacting polyethylene isophthalate with an organic diisocyanate is further reacted with ethylene glycol monomethacrylate to form the above urethane prepolymer. A coating having high elongation, however, can not be obtained from the above composition.
On the other hand, high molecular weight saturated polyesters, such as polyethyleneterephthalate, polyethyleneterephthalate-isophthalate, polybutyleneterephthalate and polyethylene-2,2-dimethylpropyleneterephthalate, are used in various fields such as fibers, molding materials, films, adhesives, paints, varnishes and plasticizers, resulting in the formation of considerable large quantities of various polyester wastes in the course of the production of such products. The reclamation or utilization of such polyester wastes are highly desirable in view of the saving of resources expected.